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MINOR: simplify last known elr update #20629

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Merged
merged 2 commits into from
Oct 6, 2025
Merged

MINOR: simplify last known elr update #20629

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aa566e0
MINOR: simplify last known elr update
CalvinConfluent Oct 2, 2025
779c614
Minor
CalvinConfluent Oct 5, 2025
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6 changes: 2 additions & 4 deletions metadata/src/main/java/org/apache/kafka/controller/PartitionChangeBuilder.java
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Original file line number Diff line number Diff line change
Expand Up @@ -494,12 +494,10 @@ private void setAssignmentChanges(PartitionChangeRecord record) {

private void maybeUpdateLastKnownLeader(PartitionChangeRecord record) {
if (!useLastKnownLeaderInBalancedRecovery || !eligibleLeaderReplicasEnabled) return;
if (record.isr() != null && record.isr().isEmpty() && (partition.lastKnownElr.length != 1 ||
partition.lastKnownElr[0] != partition.leader)) {
if (record.leader() == NO_LEADER && partition.lastKnownElr.length == 0) {
// Only update the last known leader when the first time the partition becomes leaderless.
record.setLastKnownElr(List.of(partition.leader));
} else if ((record.leader() >= 0 || (partition.leader != NO_LEADER && record.leader() != NO_LEADER))
&& partition.lastKnownElr.length > 0) {
} else if (record.leader() >= 0 && partition.lastKnownElr.length > 0) {
// Clear the LastKnownElr field if the partition will have or continues to have a valid leader.
record.setLastKnownElr(List.of());
}
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42 changes: 42 additions & 0 deletions metadata/src/test/java/org/apache/kafka/controller/PartitionChangeBuilderTest.java
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Expand Up @@ -822,6 +822,48 @@ public void testEligibleLeaderReplicas_IsrShrinkBelowMinISR(short version) {
}
}

@Test
public void testEligibleLeaderReplicas_lastKnownElrShouldBePopulatedWhenNoLeader() {
PartitionRegistration partition = new PartitionRegistration.Builder()
.setReplicas(new int[] {1, 2, 3})
.setDirectories(new Uuid[] {
DirectoryId.UNASSIGNED,
DirectoryId.UNASSIGNED,
DirectoryId.UNASSIGNED
})
.setIsr(new int[] {1})
.setElr(new int[] {2})
.setLeader(1)
.setLeaderRecoveryState(LeaderRecoveryState.RECOVERED)
.setLeaderEpoch(100)
.setPartitionEpoch(200)
.build();

short version = 2; // ELR supported
Uuid topicId = Uuid.fromString("FbrrdcfiR-KC2CPSTHaJrg");

// No replica is acceptable as leader, so election yields NO_LEADER.
// We intentionally do not change target ISR so record.isr remains null.
PartitionChangeBuilder builder = new PartitionChangeBuilder(partition, topicId, 0, r -> false,
metadataVersionForPartitionChangeRecordVersion(version), 3)
.setElection(Election.PREFERRED)
.setEligibleLeaderReplicasEnabled(isElrEnabled(version))
.setDefaultDirProvider(DEFAULT_DIR_PROVIDER)
.setUseLastKnownLeaderInBalancedRecovery(true);

ApiMessageAndVersion change = builder.build().get();
PartitionChangeRecord record = (PartitionChangeRecord) change.message();

assertEquals(NO_LEADER, record.leader());
// There is no ISR update if we do not perform the leader verification on the ISR members.
assertNull(record.isr(), record.toString());
assertEquals(1, record.lastKnownElr().size(), record.toString());
assertEquals(1, record.lastKnownElr().get(0), record.toString());
partition = partition.merge((PartitionChangeRecord) builder.build().get().message());
assertArrayEquals(new int[] {1}, partition.lastKnownElr);
}


@ParameterizedTest
@MethodSource("partitionChangeRecordVersions")
public void testEligibleLeaderReplicas_IsrExpandAboveMinISR(short version) {
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